Principles of Normal and Pathologic Gait

Key Points

Human gait is a complex phenomenon that involves intricate interactions between the pelvis, hips, knees, and ankles.
Understanding human gait requires a solid knowledge of underlying physiology and biomechanical principles.
Observational gait analysis skills are essential in the evaluation of pathologic gait patterns.
Comprehending the relationship between clinical examination findings, biomechanical influences, and gait pattern observations leads to optimal orthotic intervention.

Normal Human Gait

The goal of normal human ambulation is to facilitate travel from one location to another while minimizing effort and maintaining adequate stability across a wide variety of walking conditions. Meeting the goal is made possible by complex interactions between central and peripheral neural pathways coordinating movement of the musculoskeletal system. A solid knowledge of biomechanical and physiologic principles is necessary to understand gait performance. Furthermore, appreciation of normal gait is essential to the evaluation and management of the gait deviations seen in individuals with disabling conditions. Accurate assessment and analysis of abnormal gait patterns provides an important foundation for the appropriate prescription and fitting of lower limb orthoses.

This chapter covers gait terminology as well as the kinematics, kinetics, and muscular activity characteristics of the normal human gait. The chapter also includes descriptions of common abnormal gait patterns and implications for orthotic fitting. The information contained in this chapter is confined to the description and analysis of movement taking place below the umbilicus, although trunk sway, arm swing, and head movement all play a role in both normal human gait and pathologic gait patterns.

Gait Cycle

Walking is a highly coordinated cyclical series of movements. Several developed nomenclatures describe the limb movements and are useful in understanding functional tasks of the whole limb and in providing a framework for explaining the contributions of the musculoskeletal system at individual joints. The most basic method is to divide the cyclic movement or gait cycle into two parts, a stance phase and a swing phase ( Fig. 4.1 ).

Stance phase represents the portion of the gait cycle during which the reference limb is in contact with the ground. During normal walking, this portion accounts for approximately the first 60% of the gait cycle. The second division, swing phase, occurs when the reference limb is not in contact with the ground. During normal walking, this portion accounts for approximately the latter 40% of the gait cycle. Stance phase time (duration) and swing phase time (duration) are common temporal measures of the respective length of each phase of the gait cycle.

The start and end of each phase is marked by discrete events. By convention, the starting point of the gait cycle (0% of the gait cycle) occurs at the point in time when the foot first contacts the ground. The heel typically makes contact first in normal walking. Traditional methods describing the gait cycle refer to this event as heel strike. However, first contact with the surface may not occur with the heel, especially in pathologic gait. As such, the term initial contact is recommended, because it offers greater flexibility and accuracy in defining the start of the gait cycle. The end of stance phase and start of swing phase are marked in the gait cycle by toe-off as the foot leaves contact with the ground. The initial contact for the same limb concludes swing, ends the current gait cycle (100% of gait), and is the start of the following cycle.

The Rancho Los Amigos (RLA) terminology further subdivides the gait cycle into phases that describe the specific functions. This approach has become the preferred clinical standard. The RLA nomenclature subdivides stance into five parts and swing into three parts.

Stance Phase

Initial contact, as previously described, is the point at which the foot comes in contact with the ground and serves as the starting point of stance phase and the overall gait cycle. Initial contact is an instant in time (0% of gait) rather than a true phase or function of stance.

Loading response (0%–10% of gait) starts at initial contact and lasts until the contralateral foot leaves the ground. Loading response is a period of double limb support during which the impact of initial contact is absorbed and weight is transferred rapidly onto the leading limb. Double limb support reflects any time during the gait cycle in which both limbs remain in contact with the ground. During normal gait, this period accounts for 20% of the total gait cycle, 10% at the beginning of the stance phase and 10% at the end of stance phase.

Midstance (10%–30% of gait) starts when the contralateral foot leaves the ground and lasts until the ipsilateral heel leaves the ground. During midstance the body weight moves forward, typically aligned over the foot in contact with the ground. Midstance also accounts for the start of single limb support in that only one limb is in contact with the ground while the contralateral limb is in swing phase.

Terminal stance (30%–50% of gait) begins when the ipsilateral heel leaves the ground and ends at the time of the contralateral foot initial contact with the ground. During terminal stance, the body weight continues its forward progress such that normally the heel rises as weight moves over the forefoot. Terminal stance is the second half of single limb support and accounts for a total of 40% of the total gait cycle when combined with the portion from midstance.

Preswing (50%–60% of gait) is the final phase of stance and lasts from the time of contralateral foot initial contact with the ground until the ipsilateral foot leaves the ground (toe-off). Preswing includes the second portion of double limb support in which the now trailing limb is rapidly unloaded in preparation for advancement during swing phase.

Swing Phase

Initial swing (60%–73% of gait) is the first phase of swing and encompasses the time from when the foot leaves the ground to ipsilateral foot alignment with the contralateral ankle. During initial swing the foot lifts off the ground and the limb begins its forward advancement. A critical task of initial swing is positioning the foot such that it clears the ground and any obstacles as it advances.

Midswing (73%–87% of gait) is the time from ankle and foot alignment until when the swing leg tibia becomes vertical. During midswing the advancement of the limb continues.

Terminal swing (87%–100% of gait) is the final portion of swing phase from the time the tibia reaches a vertical position until initial contact of the swing foot with the ground. During terminal swing, the limb completes its forward advancement. Normally, a period of limb deceleration occurs leading up to the initial contact.

Functional Considerations

Coordinated movement of the body is essential to normal gait performance. From a global perspective, maintaining a stable upright position while enabling progression from one limb to the next is the primary functional task and goal of bipedal ambulation. Other goals, such as mechanical or metabolic economy, may also hold inherent value. It is important to note that the following functional considerations are described separately but do not operate independently of each other.

Rockers: Pivot Points During Stance

During the stance phase of gait, the foot remains in stationary contact with the ground while the body needs to continue forward progression. Facilitating the body's progression forward requires a balance between progression and maintenance of stability. This is accomplished through a series of rockers in the ankle and foot that allow the stance limb to rotate forward sequentially while the foot remains stationary. Perry divided this progression into four distinct rockers ( Fig. 4.2 ).

Figure 4.2, Functional rockers of the foot and ankle. Progression of the limb over a stationary foot during the stance phase of gait is accomplished through motion that occurs at four functional rockers in the foot and ankle.

Heel rocker involves the heel serving as a pivot point for the foot to move from a neutral position at initial contact toward 10 degrees of plantarflexion during loading response. The pivoting action translates momentum generated during weight acceptance to initiate forward progression of the tibia.

Ankle rocker occurs at the onset of midstance as the pivot point moves from the heel to the ankle. During midstance, the tibia and more proximal aspect of the limb rotate forward at the ankle along the line of progression. This allows advancement of the stance limb and the body.

Forefoot rocker occurs as the limb moves into terminal stance as the heel comes off the ground and the pivot point shifts to the forefoot and the rounded contour of the metatarsal heads. The action of the forefoot rocker accelerates forward progression as the body weight falls beyond the area of foot support.

Toe rocker takes place during preswing as the toe serves as the final pivot point for the body's continued forward movement and transition into swing phase.

Determinants of Gait: Economy of Walking

Six determinants of gait were originally described by Saunders and Inman in 1953. These determinants were used to describe fundamental strategies for achieving the most economical gait through optimal movement of the center of gravity (CoG). In an upright human, the CoG lies just anterior to the second sacral vertebra, and as a person ambulates with a normal gait pattern, the CoG follows a smooth, sinusoidal path in the frontal, transverse, and sagittal planes. The actual CoG displacement is approximately 5 cm (2 inches) in each plane during normal gait. Decreased economy is theorized to result in excessive deviations of the CoG from the optimal path.

Descriptions of the determinants of gait vary in different references and have been revised over time. Nevertheless, the determinants provide a framework in which normal walking can be divided into three strategies at the level of the pelvis and three in the knee, foot, and ankle mechanisms ( Box 4.1 ).

1
Pelvic rotation involves forward angular rotation of the pelvis in the transverse plane of approximately 5 degrees. This motion effectively increases the length of the lower limbs and reduces downward displacement of the CoG.
2
Pelvic tilt consists of the swing limb side of the pelvis tilting downward approximately 5 degrees from a level position during single limb stance. The tilting motion decreases vertical displacement of the CoG. However, this motion also reduces the clearance available to swing the foot forward. Angular motion at other joints, primarily knee flexion, is coordinated with pelvic tilting to maintain adequate toe clearance.
3
Knee flexion to about 15-20 degrees occurs during loading response. This motion is followed by extension of the limb to about 5 degrees short of full extension in mid-stance. The knee flexion provides shock absorption and limits vertical displacement of the CoG that would otherwise occur with full extension of the lower limb.
4
Foot and 5. ankle motion focus on ankle plantarflexion after initial contact and during terminal stance. Plantarflexion early in stance allows the foot to assume a foot-flat position and decreases the rise in CoG. Plantarflexion late in stance allows the heel to rise and prevents rapid tibial progression from provoking a sudden drop in the CoG.
6
Lateral pelvic displacement shifts the CoG over the limb providing single limb support. This motion helps to attenuate the muscular effort that would otherwise be necessary to control the CoG and prevent a loss of balance.

Box 4.1

Six Determinants of Gait

1
Pelvic rotation in the horizontal plane
2
Pelvic tilt in the frontal plane
3
Knee flexion
4
and 5. Foot and ankle motion
6
Lateral displacement of the pelvis

These determinants describe fundamental strategies for achieving the most efficient gait by minimizing the movement of the center of gravity.

Lower Extremity Movement Patterns

Analysis of body movement during gait is a valuable and common practice in research and clinical environments. Measures describe global gait patterns, joint angular motions, or joint forces.

Temporal Spatial Measures

Temporal spatial measures include numerous descriptors of basic characteristics of the gait cycle. The following are a set of common terms used in analyzing gait. Some terms were introduced and defined earlier in the chapter (stance phase duration, swing phase duration, single limb support, double limb support) and are demonstrated in Fig. 4.1 . The average values vary based on factors such as walking velocity, gender, height, age, and the presence of conditions that produce pathologic gait patterns.

A stride occurs between initial contact for a limb and the subsequent initial contact of the ipsilateral (same) limb. Strides are the basic unit of the gait cycle; one stride is equivalent to one complete cycle (0%–100% of gait). The distance traveled over the stride represents the stride length, and the total time to complete the gait cycle is the stride time. Stride length averages about 1.4 m.

A step occurs between initial contact of a limb and initial contact of the contralateral (opposite) limb. Step length and step time describe distance and times for a given step in a manner similar to the description for stride. Step length averages approximately 70 cm. In addition, step width is the distance between the centers of the feet during the double limb support portion of the gait cycle when both feet are in contact with the ground. Average step width is 8 to 10 cm.

Cadence is the number of steps taken in a given period. Cadence averages 90 to 120 steps per minute in adults walking at a comfortable speed.

Velocity is the distance covered in a given period. Normal comfortable self-selected walking velocity averages 1.34 m/s.

Kinematics

Kinematic measures describe joint motions as rotations around the principle axis of the body. This chapter primarily focuses on kinematics in the sagittal plane. Fig. 4.3 provides a description of the motion (kinematics) that occurs at the hip, knee, and ankle during normal human gait in the sagittal plane.

Ankle

The ankle begins the gait cycle in a neutral position at the time of initial contact. There is rapid plantarflexion to approximately 10 degrees of plantarflexion that occurs during the loading response. This period of plantarflexion is followed by a time of gradual dorsiflexion that continues through the midstance and terminal stance phases. Peak dorsiflexion of 10 degrees occurs just before the preswing phase. During preswing, the ankle begins to plantarflex rapidly before the foot leaves contact with the floor. This plantarflexion continues into early swing and reaches a maximum of 20 degrees before the ankle moves back into a neutral position, which is maintained during the remainder of the swing phase.

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